The present invention relates to a bidirectional DC/AC inverter, and more particularly to control for a bidirectional DC/AC inverter to switch between an operation of charging a battery and an operation of outputting alternating-current power.
FIG. 3 is a view of an existing bidirectional DC/AC inverter. The bidirectional DC/AC inverter 30 includes a filter 34, a bridge circuit 39, a bridge circuit 45, a bridge circuit 51, a condenser 53, a coil 54, a plug 55, an outlet 56, and a relay 57. The filter 34 includes coils 31 and 32 and a condenser 33. The bridge circuit 39 includes four switching devices 35 through 38 and is connected to the filter 34. The bridge circuit 45 includes four switching devices 41 through 44 and is connected to the bridge circuit 39 through a condenser 40. The bridge circuit 51 includes four switching devices 47 through 50 and is connected the bridge circuit 45 through a transformer 46. The condenser 53 and the coil 54 are disposed between the bridge circuit 51 and a battery 52. The relay 57 electrically connects the bridge circuit 39 to the plug 55 through the filter 34 when the battery 52 is charged. The relay 57 connects the bridge circuit 39 to the outlet 56 through the filter 34 when the bidirectional DC/AC inverter 30 outputs alternating-current power. The switching devices 35 through 38, the switching devices 41 through 44 and the switching device 47 through 50 are, for example, insulated gate bipolar transistors (IGBTs), and a diode is connected in parallel to each switching device. The plug 55 is connected to the outlet 59 of an external power source 58 when the battery 52 is charged. The outlet 56 is connected to the plug 61 of an external load 60 when the bidirectional DC/AC inverter 30 outputs the alternating-current power.
The bidirectional DC/AC inverter 30 alternately turns on and off the switching devices 41 and 44 and the switching devices 42 and 43 of the bridge circuit 45 when the battery 52 is charged. More specifically, when the battery 52 is charged, alternating-current power inputted from the power source 58 into the bridge circuit 39 through the outlet 59, the plug 55, the relay 57 and the filter 34 is rectified by the diodes connected in parallel to the switching devices 35 through 38 of the bridge circuit 39 and smoothed by the condenser 40, thus being converted into direct-current power. And then, the direct-current power is converted into alternating-current power by the bridge circuit 45 and outputted to the bridge circuit 51 through the transformer 46. Sequentially, the alternating-current power is rectified by the diodes connected in parallel to the switching devices 47 through 50 of the bridge circuit 51 and smoothed by the condenser 53, thus being converted into direct-current power. Lastly, the direct-current power is supplied to the battery 52 through the coil 54.
In supplying alternating-current power to the load 60, the bidirectional DC/AC inverter 30 alternately turns on and off the switching devices 47 and 50 and the switching devices 48 and 49 of the bridge circuit 51 and alternately turns on and off the switching devices 35 and 38 and the switching devices 36 and 37 of the bridge circuit 39. More specifically, when the alternating-current power is supplied to the load 60, direct-current power obtained from the battery 52 is converted into alternating-current power by the bridge circuit 51 and outputted to the bridge circuit 45 through the transformer 46. And then, the alternating-current power is rectified by the diodes connected in parallel to the switching devices 41 through 44 of the bridge circuit 45 and smoothed by the condenser 40, thus being converted into direct-current power. Lastly, the direct-current power is converted into alternating-current power by the bridge circuit 39 and supplied to the load 60 through the filter 34, the relay 57, the outlet 56 and the plug 61.
The bidirectional DC/AC inverter 30 drives the bridge circuit 45 in charging the battery 52 and the bridge circuit 39 and the bridge circuit 51 in outputting alternating-current power (cf. Japanese Patent Application Publication No. 2001-37226).
However, current inputted to the inverter 30 when the battery 52 is charged or current to be outputted from the inverter 30 when the inverter 30 outputs the alternating-current power flows through the relay 57. Thus, the bidirectional DC/AC inverter 30 requires large-sized relay 57, with the result that the bidirectional DC/AC inverter 30 becomes large in size.
The present invention is directed to a bidirectional DC/AC inverter which prevents its size from becoming large.